Fuel-cell electric vehicles, which are equipped with fuel cells that generate electricity by electrochemical reaction of hydrogen with oxygen in the air, the electricity generated by the fuel cells being supplied to motors and used as driving force, have recently been receiving attention as countermeasures against the depletion of petroleum fuel and the demand for reductions in toxic gas emission. Resin tanks including resin liners, the outsides of which are reinforced with carbon-fiber-reinforced plastics, have been studied as tanks for high-pressure hydrogen to be mounted on automobiles. Conventional resin tanks, however, disadvantageously undergo deformation or breakage with repeated charging and discharging of high-pressure hydrogen. This is because hydrogen, for its small molecular size, readily permeates through the resins as compared, for example, to natural gas, which has a relatively large molecular size, and high-pressure hydrogen, as compared to hydrogen at atmospheric pressure, may be accumulated in the resins in larger amounts.
For example, a hydrogen tank liner material comprising a polyamide resin composition containing a polyamide 6, a copolyamide, and an impact modifier is disclosed as a hydrogen tank liner material having excellent gas barrier properties and high impact resistance at low temperatures (see JP 2009-191871 A, for example).
For example, a polyamide resin composition comprising a polyamide 6 resin, a polyamide 610 resin, an ethylenic ionomer resin, and an ethylenic copolymer elastomer resin is disclosed as a polyamide resin composition suitable for use for fuel tanks, fuel delivery pipes, and other applications and having so excellent blow molding properties and low-temperature toughness that are suitable for hollow blow molding (see JP 2007-204674 A, for example).
For example, a gas storage tank liner comprising a polyamide, a nucleating agent, and a polymer composition containing an impact resistance modifier is disclosed as a gas storage tank liner having excellent gas barrier properties (see JP 2014-501818 A, for example).
Molded articles exposed to high-pressure hydrogen are produced, for example, by injection molding. In injection-molded articles produced by multipoint gate systems or metallic insert systems and injection-molded articles having structural ribs or openings, fragile portions called welds tend to be formed at portions in a mold where molten resin flows meet. At welds, V-shaped grooves called weld lines may be formed due to adhesion failure, resulting in poor appearances. In addition, strength and toughness may be reduced due to stress concentrations (notch effects). Thus, high weld properties are required in designing molded articles.
The hydrogen tank liner disclosed in JP 2009-191871 A, however, has disadvantages in that permeation of hydrogen gas and absorption of hydrogen into the resin are likely to occur, and the hydrogen tank liner suffers failure points with repeated charging and discharging of high-pressure hydrogen. In addition, the polyamide resins have low compatibility, and the weld properties are poor.
The resin composition disclosed in JP 2007-204674 A, although having excellent low-temperature toughness, has disadvantages in that permeation of hydrogen gas and absorption of hydrogen into the resin are likely to occur, and the hydrogen tank liner suffers failure points with repeated charging and discharging of high-pressure hydrogen. In addition, the polyamide resins have low compatibility, and the weld properties are poor.
The gas storage tank liner disclosed in JP 2014-501818 A, although having excellent resistance to helium gas permeation, has disadvantages in that permeation of hydrogen gas and absorption of hydrogen into the resin are likely to occur, and the hydrogen tank liner suffers failure points with repeated charging and discharging of high-pressure hydrogen. In addition, the dispersibility of the nucleating agent in the polyamide and the adhesion of the polyamide to the nucleating agent are low, and the weld properties are poor.
It could therefore be helpful to provide a polyamide resin composition that can provide a molded article having excellent weld properties and less likely to suffer failure points despite repeated charging and discharging of high-pressure hydrogen.